Two heat exchanger concepts for cooling gases in EGR systems are described in the state of the art.
In monoblock type exchangers, the bundle of tubes is integrally attached to the shell at its ends by means of welding. Its manufacture, therefore, is simple: there is no need for assembling by means of metal joints and O-ring joints, with the subsequent cost savings and size reduction of the exchanger. However, the temperature differences reached by both components in operation give rise to also different degrees of expansion, and since both components are fixed to one another stresses which could cause them to break are produced, thereby reducing the thermal fatigue life of the part.
In turn, the bundle of tubes is independent of the shell in floating core type exchangers. The tubes are welded at each of their ends to a component referred to as a baffle, which in turn are connected to the shell by means of metal joints and O-ring joints. These exchangers solve the thermal fatigue problem in the following manner: one of the baffles is attached to the shell by means of an O-ring joint which assures leak-tightness while at the same time enables the tubes to freely expand at this end in the axial direction. The end at which the O-ring joint is located and at which the bundle of tubes can freely expand is usually the end closest to the entrance of coolant in the shell, because the O-ring joint is made of an elastomeric material that does not withstand such high temperatures like metal does. The greatest difficulty in the design, which is the result of the more complicated geometry of the shell, of the different production steps required by the manufacturing process, such as welding the bundles of tubes and the baffles and the process of assembling them in the shell, and of the high cost of some of the materials, such as the sealing gaskets, means that floating core exchangers are considerably more expensive, up to 20% or 30%, than monoblock exchangers.
The present invention describes a heat exchanger and a process for manufacturing it which combines the thermal fatigue strength of floating core exchangers with the compact, simple and more economical design of monoblock exchangers resulting from, among others, the lower number of necessary manufacturing steps.